The beneficial effects of diastolic balloon pumping have been well-documented in patients with ischemic left ventricular low-output cardiac failure. Hemodynamic improvement occurs as a result of the increase in coronary perfusion pressure from augmentation of diastolic blood pressure, and as a result of reduction of impedence to left ventricular ejection. Despite widespread acceptance of intra-aortic balloon pumping there has been only limited laboratory investigation of application of the principles of diastolic balloom pumping to assistance of the failing right ventricle. This study was designed to evaluate the effectiveness of intrapulmonary artery balloon pumping (IPABP) in improving the hemodynamic state in animals with a chronic process affecting right ventricular function. Hemodynamic improvement from IPABP would occur by reduction of impedence to right ventricular ejection derived from rapid presystolic balloon deflation.